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Tylosaurus Proriger

Tylosaurus may have ruled the Late Cretaceous seas because all other would-be competitors, such as ichthyosaurs, were already extinct. Though they evolved from terrestrial lizards, the paddle-like limbs of giant mosasaurs like Tylosaurus were useless on land.

Fast Facts

Mosasaurs gave birth to live young. A baby Tylosaurus was 3 to 6 ft (1 to 2 m) long—small enough for predatory fish and sharks to eat.

Size relative to a bus:

Tylosaurus was the deadliest hunter of the ancient seas, ready to seize and kill just about any smaller creature that crossed its path with true jaws of death—lined on each side with two rows of pointy, cone-shaped teeth. Tylosaurus used its snout to locate prey, which, once inside the mosasaur's menacing jaws, was swallowed whole. When the sea monster opened wide for the final gulp, two extra rows of teeth on the roof of its mouth allowed crippled captives no escape.

Tylosaurus grew more than 45 feet (14 meters) long, making it the largest of the marine reptiles called mosasaurs. Like all mosasaurs, a long and muscular, vertically flattened tail powered Tylosaurus through the water, allowing it to ambush its prey with rapid bursts of acceleration. Paddle-like limbs helped steer the slim body covered in lizard-like scales through the water.

Preserved stomach contents indicate a diet heavy on fish, but seabirds, sharks, plesiosaurs, and other mosasaurs also failed to escape Tylosaurus's lethal grip. Though not a dinosaur, Tylosaurus lived alongside them and went extinct at around the same time. Many Tylosaurus remains have been found in Kansas, which was once covered by a large ocean called the Western Interior Seaway.